GOCE launchedESA launches first Earth Explorer mission GOCE

Satellit zur Messung des Schwerefelds gestartet<br />
This afternoon, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite developed by the European Space Agency (ESA) was lofted into a near-sunsynchronous, low Earth orbit by a Rockot launcher lifting off from the Plesetsk cosmodrome in northern Russia.

Der Satellit GOCE ist seit dem 17. März 2009 im All (Zeichnung: ESA)

With this launch, a new chapter in the history of Earth observation in Europe has begun. GOCE is the first of a new family of ESA satellites designed to study our planet and its environment in order to enhance our knowledge and understanding of Earth-system processes and their evolution, to enable us to address the challenges of global climate change. In particular, GOCE will measure the minute differences in the Earth's gravity field around the globe.

The Russian Rockot launcher, derived from a converted ballistic missile, lifted off at 15:21 CET (14:21 GMT) and flew northward over the Arctic. About 90 minutes later, after one orbital revolution and two Breeze-KM upper-stage burns, the 1052 kg spacecraft was successfully released into a circular polar orbit at 280 km altitude with 96.7 degree inclination to the Equator. The launch was procured from Eurockot Launch Services, a German/Russian company based in Bremen, Germany. Contact with GOCE was established via ESA's tracking station in Kiruna, Sweden, shortly after separation. The spacecraft is now under the control of ESA's teams at its European Space Operations Centre in Darmstadt, Germany.

For 24 months GOCE will collect three-dimensional gravity data all over the globe. The raw data will be processed on the ground to produce the most accurate map of the Earth's gravitational field to date and to refine the geoid: the actual reference shape of our planet. Precise knowledge of the geoid, which can be considered as the surface of an ideal global ocean at rest, will play a very important role in further study of our planet, its oceans and atmosphere. It will serve as the reference model for our measurement and modelling of sea-level change, ocean circulation and polar ice cap dynamics.

The data collected by GOCE will yield accuracy of 1 to 2 cm in the geoid altitude and 1 mGal for the detection of gravity-field anomalies (mountains, for instance, usually cause local gravitational variations ranging from tens of milligals to approximately one hundred). The spatial resolution will be improved from several hundreds or thousands of kilometres on previous missions to 100 km with GOCE.

In order to get the maximum performance from the Gradiometer, GOCE is designed to provide a highly stable and undisturbed environment, despite its low-altitude orbit which forces the spacecraft to endure slight but significant drag from the uppermost layers of the atmosphere. This is the main reason for its slender 5 metre-long arrowhead aerodynamic shape design.

The spacecraft also incorporates two low-power xenon ion engines, one primary and one backup, each able to deliver 1 to 20 milli-Newtons of thrust (the force equivalent to our exhaling). These thrusters will be used to make real-time compensation for atmospheric drag, based on the mean acceleration detected by the two accelerometers mounted along the velocity axis.